Research Bits: Apr. 2

Flexible electronics: Stretchy, sensitive circuits; washable photovoltaics; bendable energy storage.


Stretchy, sensitive circuits

Researchers from Stanford University developed skin-like, stretchable integrated circuits capable of driving a micro-LED screen with a refresh rate of 60 Hz and detecting a braille array that is more sensitive than human fingertips.

The stretchable transistors are made from semiconducting carbon nanotubes sandwiched between soft elastic electronic materials. The transistors and circuits are patterned onto a stretchable substrate, along with stretchable semiconductor, conductor, and dielectric material.

In one demonstration, the researchers were able to fit more than 2,500 sensors and transistors into a square centimeter, creating an active-matrix tactile array over ten times more sensitive than human fingertips.

An active-matrix sensor array attached to a human finger. (Credit: Donglai Zhong and Can Wu of Bao Group in Stanford University)

“Preliminary results demonstrate that our transistor can be used to drive commercial displays commonly used in computer monitors, for example,” said Can Wu, a postdoctoral researcher at Stanford, in a statement. “And for biomedical applications, a high-density, soft, and conformable sensing array could allow us to sense human body signals, such as from our brains and muscles, at a large scale and fine resolution. This could lead to next-generation brain-machine interfaces that are both high-performance and biocompatible.” [1]

Washable photovoltaics

Researchers from the RIKEN Center for Emergent Matter Science, University of Tokyo, and Huazhong University of Science and Technology developed an organic photovoltaic film that is both waterproof and flexible. The solar film could be placed on clothing and still function after being rained on or washed.

Key was reducing the number of layers required to make the photovoltaic film, as the addition of waterproofing layers can compromise flexibility. The anode layer, a silver electrode, was deposited directly onto the active layers, providing improved adhesion. A thermal annealing process was then applied, resulting in a film 3 micrometers thick.

In tests, the film retained 89% of its initial performance after being immersed completely in water for four hours. A film that was stretched by 30% 300 times underwater retained 96% of its performance. It also survived a trip through a washing machine. [2]

Bendable energy storage

Researchers from Pohang University of Science and Technology, Sungkyunkwan University, and University of Seoul found a way to synthesize bendable energy storage devices made of mesoporous metal oxides (MMOs) at lower temperatures, making them compatible with flexible substrates.

MMOs have pores ranging from 2nm to 50nm, giving them an extensive surface area that makes them well suited for energy storage. Typically, fabricating them requires temperatures above what plastic substrates can withstand. However, by utilizing the synergetic effect of heat and plasma, the researchers were able to synthesize MMOs of vanadium oxide, titanium dioxide, tungsten trioxide, and other high-performance energy storage materials at temperatures of 150-200°C. The fabricated devices could be bent thousands of times without losing energy storage performance. [3]


[1] Zhong, D., Wu, C., Jiang, Y. et al. High-speed and large-scale intrinsically stretchable integrated circuits. Nature 627, 313–320 (2024).

[2] Xiong, S., Fukuda, K., Nakano, K. et al. Waterproof and ultraflexible organic photovoltaics with improved interface adhesion. Nat Commun 15, 681 (2024).

[3] K.-W. Kim, H. Seok, S. Son, S.-J. Park, C. Yang, D. Lee, H.-C. Lee, J. Mun, H.-J. Yeom, M. Y. Yoon, B. Park, S. H. Kim, C. Jo, H. C. Moon, T. Kim, J. K. Kim, Low-Temperature, Universal Synthetic Route for Mesoporous Metal Oxides by Exploiting Synergistic Effect of Thermal Activation and Plasma. Adv. Mater. 2024, 2311809.

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